In a conventional apparatus for the electroplating of a rotogravure printing cylinder, it is customary to rotate the cylinder (electrically charged as a cathode) in a tank filled with an electrolyte bath and copper bars or copper nuggets (electrically charged as an anode), as disclosed in U.S. Pat. No. 4,352,727 issued to Metzger, and incorporated by reference herein (wherein the copper nuggets are supported in a set of baskets made of titanium or of a plastic material and disposed around each side of the cylinder), or simply a plating solution.
In the arrangement shown in U.S. Pat. No. 4,352,727, the top edge of the respective baskets are disposed below the surface of the electrolyte bath so as to ensure free circulation of constantly refreshed (i.e. filtered) electrolytic fluid or solution. Electrolytic fluid is pumped into the tank from a manifold adjacent to the bottom of one of the baskets, in the direction of cylinder rotation. The top of the rotating cylinder to be plated is disposed slightly above the surface level of the electrolytic fluid so that a washing action occurs as the surface of the cylinder breaks across the surface of the electrolyte. Ions move from the copper bars or nuggets through the electrolytic fluid to the surface of the rotating cylinder during the plating process (or in the reverse direction in the deplating process). Where plating is done directly from a plating solution, ions move directly from the solution to the surface of the rotating cylinder.
Over time, refinements of this system have facilitated satisfactory control of the plating process, to achieve the desirable or necessary degree of consistent plating and uniformity in the plated surface of the cylinder. However, the complete process is comparatively slow, and extra polishing steps may be necessary after plating in order to produce a desirable uniform surface (e.g. roughness on grain structure) on the cylinder. According to the known arrangement, the overall efficiency of the process necessary to produce a suitably uniform plated surface on the cylinder can be adjusted either by reducing the current density, which increases the plating time but reduces the number or duration of additional polishing steps, or by increasing the current density, which reduces the plating time but increases the number or duration of additional polishing steps.
Furthermore, in the known arrangement, during operation, a copper sludge may tend to accumulate on and about the cylinder during the plating process, forming uneven and undesirable copper deposits, typically in areas of low current density (such as furthest apart from the copper cylinder). A copper sludge may also build up between the contact surfaces of the titanium baskets or lead contacts. Moreover, other surfaces may become fouled with sludge and other matter.
Ultrasonic wave energy has been used successfully in surface cleaning applications. The long-known advantages in using ultrasonic energy in electroplating have also been described in such articles as "Ultrasonics in the Plating Industry", Plating, pp. 141-47 (August 1967), and "Ultrasonics Improves, Shortens and Simplifies Plating Operations," MPM, pp. 47-49 (March 1962), both of which are incorporated by reference herein. It has been learned that ultrasonic energy may advantageously be employed to improve the quality (e.g. uniformity and consistency of grain structure) of a plating process by providing for uniformity and efficiency of ion movement. In other applications, it has been found that copper can be plated onto a surface in a production system using ultrasonic energy at up to four times the rate ordinarily possible. It has also been found that the use of ultrasonic energy in an electroplating process provides an increase in both the anode and cathode current efficiency, and moreover, the practical benefit of faster plating with less hydrogen embrittlement (e.g. with less oxidation of the hydrogen on the plating and deplating surfaces).
Accordingly, it would be advantageous to have an apparatus configured to capitalize on the advantages of substantially removing or eliminating from the plating tank any solid material that is soluble or vulnerable to dissolution in the plating solution. It would further be advantageous to have a rotogravure cylinder apparatus employing a non-dissolvable anode to substantially reduce or eliminate the build-up of copper (or other) sludge during the plating process and obtain a more uniform and consistent grain structure on the plated surface of the cylinder. It would also be advantages to have an apparatus configured to employ an anode to enable the usage of an increased current density for faster plating with minimum polishing steps. It would also be advantages to have an apparatus configured to use ultrasonic energy in plating a rotogravure cylinder in order to obtain a more uniform and consistent grain structure on the plated surface of the cylinder through a more efficient process. It would further be advantageous to have a rotogravure cylinder plating apparatus employing ultrasonic energy to eliminate the build-up of copper (or other) sludge during the plating process.